1. Technical Field of the Invention
The present invention relates in general to hand truck, and more particularly to a hand truck with an automatic height adjusting load platform and a kit for modifying a hand truck to include an automatic height adjusting load platform.
2. Description of the Related Art
Hand trucks and other hand operated material moving devices have been widely used for numerous years. A hand truck is usually comprised of a substantially vertical frame, a load platform or shelf secured to the bottom portion of the frame that extends outward and perpendicular to the frame, and wheels generally placed near the load platform and on the opposite side of the frame as the load platform. A user slides the load platform under an object to be moved, or alternatively sets an object upon the load platform, then rotates the vertical frame such that the load platform is raised into the air and only the wheels contact the surface immediately below the hand truck. By balancing the hand truck on its wheels, an operator can easily move an otherwise heavy object from one position to another.
While the hand truck enjoys popular success today, it has been recognized by the present inventor that a user must bend or stoop to place objects or remove objects from the load platform. The bending or stooping motion can be eliminated or reduced with an automatic mechanism incorporated into the hand truck such that the height of the load platform automatically adjusts with reference to; the weight and height of the material loaded thereupon. The present inventor has further recognized that a load placed on a hand truck can be of significant weight. Should a load become unstable either due to tipping or the like, a sudden reduction in weight on the load platform could cause the platform to raise too quickly.
The present inventor has additionally recognized that an adjustable shelf in a raised position may be awkward for certain transportation needs. For example, it is not uncommon to secure hand trucks to the exterior of a vehicle by wedging the load platform into a predetermined position. This is difficult or impossible to accomplish with a raised platform.
Accordingly, there is a need for a hand truck with an automatic height adjusting load platform that incorporates a braking mechanism to prevent the load platform from transitioning too quickly due to sudden changes in load. Preferably, the load platform should be removable and repositionable. Further, the adjustable load platform should optionally be in kit form for retrofitting currently existing hand trucks.
This need is met by the present invention wherein a hand truck includes a automatic height adjusting load platform. A shelf guide secured between the frame upper and lower portions provides a substantially vertical shaft positioned between the vertical frame members of the hand truck. The load platform is slidably mounted to the shaft and interconnected to a platform arrestor for controlling the variable shelf position. The load platform position is held in a raised position while under no load conditions by the platform arrestor. For example, one of many possible options is to configure the load platform to rest at approximately waist level. A user places an article such as a package or carton on the raised platform. In response to the weight of the article, the platform lowers, but the downward motion of the platform is inhibited by the platform arrestor. Preferably, the platform arrestor is configured such that the distance the platform will drop due to the weight of the load is proportional to the height of the article placed upon the platform. Of course this presupposes that the hand truck will be used to haul items of consistent dimension and weight, but in industries such as beverage distribution, this is often the case. Thus the top of the article first placed upon the load platform is now substantially at the unloaded, load platform level. This process can continue until the platform is lowered to the bottom of the shaft that the platform is slidably mounted to. If the load platform was initially at waist level, and the proper size and weight items were being loaded, the user is never required to bend or stoop. As, articles are removed, under normal conditions, the platform arrestor will control the rate at which the platform returns to its raised position. Further, where the load becomes unstable due to tipping or the like, the platform arrestor prevents the load platform from transitioning upward too quickly. The load platform is further detachable for applications where having the platform in a raised position is undesirable.
In accordance with one aspect of the present invention, a hand truck having a substantially vertical frame of spaced parallel bars includes a toe platform extending substantially outward from the frame, and wheels connected to the frame lower portion opposite the toe platform. A shelf guide is secured to the frame to provide a shaft. A load platform slidably mounts to the shaft to provide a surface for placing articles. A platform arrestor is secured to the frame lower portion, for example along the shaft axle, and provides a control to adjust the position of the adjustable load platform. The platform arrestor is connect further, to a pulley assembly at its upper portion. A cable connected between the load platform and the shelf guide upper portion extends over the shelf guide upper portion, downward and through the pulley, and upward to the shelf guide upper portion where it is secured. At least one pulley is further included on the shelf guide upper portion to guide the cable.
The shelf guide of the hand truck includes top mounting bracket secured to the frame between the spaced parallel bars and includes at least one bracket pulley. The shelf guide lower portion is secured to the frame lower portion, for example, by a bracket mounted to the toe plate. A substantially vertical shaft is secured between the shelf guide upper portion via the top mounting bracket, and the shelf guide lower portion for engagement with the slidable load platform. It is preferable that the hand truck includes a pair of stabilizing bars placed one on either side of the shaft to aid in the alignment of larger sized loads. The load platform further includes a shelf plate slidably mounted to the shelf guide and a platform releasably secured to the shelf plate.
Preferably, the platform arrestor includes one or more springs connected between the frame lower portion and the first pulley, and additionally, one or more spring brakes connected between the frame lower portion and the first pulley. The springs may be optionally releasably connected so as to be able to adjust for various loading conditions. The brake can comprise a hydraulic cylinder for example positioned inside the spring.
In accordance with another aspect of the present invention, a kit of components is provided for adding an adjustable load platform to a host hand truck. The host hand truck has in its original configuration, a substantially vertical frame having spaced parallel bars, a frame upper portion and a frame lower portion. The frame lower portion includes a toe platform extending substantially outward from the frame and one or more wheels connected to said frame lower portion opposite said toe platform. The kit of components comprises a shelf guide having a shelf guide upper portion and a shelf guide lower portion. The shelf guide upper portion is secured to the frame upper portion of the host hand truck, while the shelf guide lower portion is secured to the frame lower portion of the host hand truck. Further, a load platform is slidably mounted to the shelf guide. A platform arrestor having a platform arrestor first end and a platform arrestor second end is included for controlling the shelf height. The platform arrestor is connected to the host hand truck frame lower portion. A first pulley is connected to the platform arrestor first end. To attach the load platform to the platform arrestor on the host hand truck, a cable is connected between the load platform and the shelf guide upper portion. The cable extends over the shelf guide upper portion, downward and through the first pulley which is connected to the upper portion of the platform arrestor, and upward terminating by attachment to the shelf guide upper portion. The kit further includes a pair of stabilizing bars connected between the frame upper portion and the frame lower portion for balancing loads held in a raised position.
It is an object of the present invention to provide a hand truck having a height adjustable load platform that is initially in a raised position, and automatically adjusts to the weight of the objects placed upon it.
It is another object of the present invention to provide a hand truck that includes a braking device to prevent sudden oscillations or velocity changes in the load platform due to sudden changes in loading.
It is yet another object of the present invention to provide a hand truck that allows the height adjustable load platform to be repositionable or removable.
It is yet another object of the present invention to provide a hand truck kit that allows a height adjustable load platform to be retrofitted to conventional hand trucks.
Other objects of the present invention will be apparent in light of the description of the invention embodied herein.